A friend of mine works as a sales representative and had a short sexual relationship with a member of staff in one of the stores he visited, they only slept together once however they stayed in contact and were friends although she would flare up at him some times and it was obvious she was quite obsessed with him. They had a big argument and after he suggested they spend a night in a hotel (she had been wanting him to go on holiday which I told him was a bad idea) she sent messages in response which were very out of character saying he was crossing boundaries, she wasn't interested in him romantically and did not want to have sex with him etc. She then complained at her work that he was sexually harassing her and showed these specific messages to her employer. Her employer contacting his company and he received a letter which was an immediate termination of conract due to gross misconduct which also said that they saw confirmation messages. I can post the email if people require it.

He was never contacted by his employee to ask for his side of the story, he has literally hundreds of whatsapp and text messages showing that he was clearly not sexually harassing her, however he is not sure how to proceed. He has worked at the company for just under a year (which i know is an issue) and he was told by ACAS (by an uninterested advisor) that theres nothing he can do. He has not contacted them yet as he was hoping ACAS would give him advice.

He's not sure what to do now as he wants to clear his name as he has evidence against the accusation. Can anyone advise what he should do next? It seems crazy that someone can make an accusation and have such a dramatic impact on someone's life. He's now banned from the chain of stores and been sacked with immediate effect yet no-one has even spoken to him or asked for his side of the story. I myself have messages I sent him warning that I thought she was the sort of person who would do something like this! There is a lot of evidence of us discussing her being infactuated too.

You miss the point, HL. The employer may very easily have a hard and fast rule against sales employees having relationships with the staff of customers. If so, he would be dismissed irrespective of any harrassment allegation. The relationship would be enough. It may well be a fairly common rule.